Metal wood club with improved hitting face

ABSTRACT

A golf club head having selectively oriented zones of relatively high flexural stiffness is disclosed. The hitting face is configured and dimensioned so that it includes an inner zone and a concentric intermediate zone. The inner zone has relatively high flexural stiffness and the intermediate zone has relatively lower flexural stiffness. The inner zone may have an elliptical shape or a substantially parallelogram shape. Preferably, the inner zone has a shape that comprises a major axis and a minor axis and the major axis aligns substantially in the direction of high heel to low toe. This arrangement of inner and intermediate zones creates a gradient of flexural stiffness in the direction of high toe to low heel and produces a desirable manipulation COR in that direction. This area of high coefficient of restitution advantageously coincides with the ball impact pattern that golfers typically make on the hitting face. The hitting face also comprises a measurement zone wherein the lowest COR is at least 93% of the highest COR.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 09/551,771 filed on Apr. 18, 2000 and now U.S. Pat.No. 6,605,007. The disclosure of the parent patent application isincorporated herein in its entirety.

FIELD OF THE INVENTION

The present invention relates to an improved golf club head. Moreparticularly, the present invention relates to a golf club head with animproved striking face having a zone of high coefficient of restitutionaligned in a predetermined orientation.

BACKGROUND

The complexities of golf club design are well known. The specificationsfor each component of the club (i.e., the club head, shaft, hosel, grip,and subcomponents thereof) directly impact the performance of the club.Thus, by varying the design specifications, a golf club can be tailoredto have specific performance characteristics.

The design of club heads has long been studied. Among the more prominentconsiderations in club head design are loft, lie, face angle, horizontalface bulge, vertical face roll, face progression, face size, solecurvature, center of gravity, material selection, and overall headweight. While this basic set of criteria is generally the focus of golfclub engineering, several other design aspects must also be addressed.The interior design of the club head may be tailored to achieveparticular characteristics, such as the inclusion of hosel or shaftattachment means, perimeter weights on the face or body of the clubhead, and fillers within hollow club heads.

Golf club heads must also be strong to withstand the repeated impactsthat occur during collisions between the golf club and the golf ball.The loading that occurs during this transient event can accelerate thegolf ball to several orders of magnitude greater than gravity. Thus, theclub face and body should be designed to resist permanent deformation orcatastrophic failure by material yield or fracture. Conventional hollowmetal wood drivers made from titanium typically have a uniform facethickness exceeding 0.10 inch to ensure structural integrity of the clubhead.

Players generally seek a metal wood driver and golf ball combinationthat delivers maximum distance and landing accuracy. The distance a balltravels after impact is dictated by the magnitude and direction of theball's translational velocity and the ball's rotational velocity orspin. Environmental conditions, including atmospheric pressure,humidity, temperature, and wind speed, further influence the ball'sflight. However, these environmental effects are beyond the control ofthe golf equipment manufacturer. Golf ball landing accuracy is driven bya number of factors as well. Some of these factors are attributed toclub head design, such as center of gravity and club face flexibility.

The United States Golf Association (USGA), the governing body for therules of golf in the United States, has specifications for theperformance of golf balls. These performance specifications dictate thesize and weight of a conforming golf ball. One USGA rule limits the golfball's initial velocity after a prescribed impact to 250 feet per second±2% (or 255 feet per second maximum initial velocity). To achievegreater golf ball travel distance, ball velocity after impact and thecoefficient of restitution of the ball-club impact must be maximizedwhile remaining within this rule.

Generally, golf ball travel distance is a function of the total kineticenergy imparted to the ball during impact with the club head, neglectingenvironmental effects. During impact, kinetic energy is transferred fromthe club and stored as elastic strain energy in the club head and asviscoelastic strain energy in the ball. After impact, the stored energyin the ball and in the club is transformed back into kinetic energy inthe form of translational and rotational velocity of the ball, as wellas the club. Since the collision is not perfectly elastic, a portion ofenergy is dissipated in club head vibration and in viscoelasticrelaxation of the ball. Viscoelastic relaxation is a material propertyof the polymeric materials used in all manufactured golf balls.

Viscoelastic relaxation of the ball is a parasitic energy source, whichis dependent upon the rate of deformation. To minimize this effect, therate of deformation must be reduced. This may be accomplished byallowing more club face deformation during impact. Since metallicdeformation may be purely elastic, the strain energy stored in the clubface is returned to the ball after impact thereby increasing the ball'soutbound velocity after impact.

A variety of techniques may be utilized to vary the allowabledeformation of the club face, including uniform face thinning, thinnedfaces with ribbed stiffeners and varying thickness, among others. Thesedesigns should have sufficient structural integrity to withstandrepeated impacts without permanent deformation of the club face. Ingeneral, conventional club heads also exhibit wide variations in thecoefficient of restitution depending on the impact location on the faceof the club. Furthermore, the accuracy of conventional clubs is highlydependent on impact location.

It has been reported in F. Werner and R. Greig, How Golf Clubs ReallyWorks and How to Optimize Their Designs, Ch. 4, pp. 17–21 (2000) that atypical distribution of golf ball hits on the face of a driver clubfollows an elliptical pattern with its major axis orientating in adirection from high toe to low heel. The size of the hit distributiondepends on the handicap of the golfer. Players with low handicap havesmaller elliptical distribution and players with high handicap havelarger elliptical distribution. These authors also patented golf clubsthat have an elliptical outer hitting face that aligns in the directionof high toe to low heel. See U.S. Pat. No. 5,366,233, entitled “GolfClub Face for Drivers,” issued on Nov. 22, 1994. However, there is noteaching to align the coefficient of restitution of the golf club headto the ball impact pattern.

SUMMARY OF THE INVENTION

The present invention relates to a golf club head adapted for attachmentto a shaft. The head includes a hitting face and a body. The hittingface is configured and dimensioned so that it includes at least an innerzone and a concentric intermediate zone. The inner zone has relativelyhigh flexural stiffness and the intermediate zone has lower flexuralstiffness. Preferably, the inner zone has a shape that comprises a majoraxis and a minor axis and the major axis aligns substantially in thedirection of high heel to low toe. The inner zone can have an ellipticalshape or a substantially parallelogram shape. The inner zone andintermediate zone may have same shape or different shape.

This arrangement of inner and intermediate zones forms an area ofrelatively high flexural stiffness in the direction of high heel to lowtoe, thereby creating high resilience in the direction of high toe tolow heel. In other words, this arrangement creates a gradient offlexural stiffness in the direction of high toe to low heel, andproduces a desirable effect of manipulating resilience or highercoefficient of restitution (COR) in that direction. This area ofimproved coefficient of restitution advantageously coincides with theball impact pattern that golfers typically make on the hitting face.

The inventive club head encompasses a measurement zone that exhibitshigh COR where the lowest COR is at least 93% of the peak COR withinthis measurement zone. The measurement zone is defined by a rectanglehaving the dimensions of 0.5 inch by 1.0 inch, and the COR values aremeasured at the corners of the rectangle, the mid-points of the sidesand the geometric center of the rectangle. The geometric center of themeasurement zone preferably coincides with the geometric center of theface of the club.

The above is accomplished by providing the inner zone with a firstflexural stiffness and the intermediate zone with a second flexuralstiffness. Flexural stiffness is defined as Young's modulus or elasticmodulus (E) times the zone's thickness (t) cubed or Et³. The firstflexural stiffness is substantially higher than the second flexuralstiffness. As a result, upon ball impact, the intermediate zone exhibitssubstantial elastic deformation to propel the ball.

In one embodiment, the first flexural stiffness is at least three timesthe second flexural stiffness. In other embodiments, the first flexuralstiffness is six to twelve times the second flexural stiffness. Morepreferably, the first flexural stiffness is greater than 25,000 lb-in.Most preferably, the first flexural stiffness is greater than 55,000lb-in. Preferably, the second flexural stiffness is less than 16,000lb-in. More preferably, the second flexural stiffness is less than10,000 lb-in.

Since the flexural stiffness is a function of material properties andthickness, the following techniques can be used to achieve thesubstantial difference between the first and second flexuralstiffness: 1) different materials can be used for each portion, 2)different thicknesses can be used for each portion, or 3) differentmaterials and thicknesses can be used for each portion.

The golf club head may further include a perimeter zone disposed betweenthe intermediate zone and the body of the club. In one embodiment, theperimeter zone has a third flexural stiffness that is at least two timesgreater than the second flexural stiffness

In the club heads discussed above, the inner, intermediate and optionalperimeter zones can have any shape that has a major axis and a minoraxis, such as elliptical, rhombus, diamond, other quadrilateral shapeswith one or more rounded corners and the like. The zones may also have asubstantially parallelogram shape. Furthermore, the club head innercavities can have a volume greater than about 100 cubic centimeters, andmore preferably a volume greater than about 300 cubic centimeters. Inother words, the club head in accordance to the present invention can beused in driver clubs and/or fairway clubs. In addition, the inner,intermediate, and perimeter zones can each have variable thickness.

Another feature of the present invention is locating the center ofgravity of the club head with respect to a Cartesian coordinate system.The origin of the Cartesian coordinate system preferably coincides withthe geometric center of the hitting face. The X-axis is a horizontalaxis positioned tangent to the geometric center of the hitting face withthe positive direction toward the heel of the club. The Y-axis isanother horizontal axis orthogonal to the X-axis with the positivedirection toward the rear of the club. The Z-axis is a vertical axisorthogonal to both the X-axis and Y-axis with the positive directiontoward the crown of the club. The center of gravity is preferablylocated behind and lower than the geometric center of the face.

In one preferred embodiment, the center of gravity is spaced from thegeometric center along the Z-axis by about −0.050 inch to about −0.150inch, and more preferably by about −0.110 inch. The center of gravity ispreferably spaced about ±0.050 inch, and more preferably about +0.015inch from the geometric center along the X-axis. The center of gravityis preferably spaced about +2.0 inches and more preferably about +1.35inches from the geometric center along the Y-axis.

The hitting face may comprise a face insert and a face support. The facesupport defines a cavity adapted to receive the face insert. The hittingface may further comprise at least one side wall, which can be a partialcrown portion or a partial sole portion. Preferably, the inner zone islocated on the face insert, and the intermediate zone may partially belocated on the face insert and partially on the face support.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred features of the present invention are disclosed in theaccompanying drawings, wherein similar reference characters denotesimilar elements throughout the several views, and wherein:

FIG. 1 is a toe side, front, perspective view of an embodiment of a golfclub head of the present invention;

FIG. 2 is a heel side, rear, perspective view of the golf club head ofFIG. 1;

FIG. 3 is a front, elevational view of the golf club head of FIG. 1;

FIG. 3A is a cross-sectional view of the face of the golf club head ofFIG. 1 along line 3A—3A; FIG. 3B shows a cross-sectional view the faceof the golf club head of FIG. 1 along line 3B—3B; FIGS. 3C and 3D arealternative embodiments of FIGS. 3A and 3B, respectively;

FIG. 4 is a top view of the golf club head of FIG. 1;

FIG. 5 is a bottom, perspective view of the golf club head of FIG. 1;

FIG. 6 is a schematic view of substantially parallelogram shaped theinner and intermediate zones;

FIG. 7 is a schematic view of the inner and intermediate zones withsubstantially parallelogram and elliptical shape;

FIG. 8 is a front, exploded view of another embodiment of the presentinvention;

FIG. 9 is a front, exploded view of another embodiment of the presentinvention; and

FIGS. 10( a)–10(c) illustrate the results from a comparative example,which compares iso-COR contour lines of conventional golf club head andof an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1–5, a first embodiment of a golf club head 10 of thepresent invention is shown. Club head 10 includes shell 12 with body 14,hitting face 16, toe portion 18, heel portion 20, sole plate 22, hosel24, bottom portion 26, crown portion 28, and rear portion 29. The soleplate 22 fits in a recess 30 (as shown in FIG. 5) in the bottom portion26 of body 14. The shell 12 and sole plate 22 create an inner cavity 31(as shown in FIG. 5). The hitting face 16 has an exterior surface 32 andan interior surface 34. The exterior surface 32 is generally smoothexcept for external grooves (which are omitted for clarity). Preferably,interior surface 34 has elevated or depressed areas to accommodate thevarying thickness of hitting face, as discussed below and shown in FIGS.3A–3D.

A golf club shaft (not shown) is attached at hosel 24 and is disposedalong a shaft axis SHA. The hosel may extend to the bottom of the clubhead or may terminate at a location between the top and bottom portionsof the head. The hosel can also terminate flush with the top portion orextend into the cavity within the head.

Inner cavity 31 of club head 10 may be empty, or alternatively may befilled with foam or other low specific gravity material. It is preferredthat the inner cavity 31 has a volume greater than 100 cubiccentimeters, and more preferably greater than 300 cubic centimeters. Inother words, the club head design in accordance to the present inventioncan be used with any driver club, as well as any fairway club.Preferably, the mass of the inventive club head is greater than 150grams but less than 250 grams.

Referring to FIGS. 1 and 3–3D, the face 16 includes an inner zone orportion 36, an intermediate zone or surrounding portion 38 adjacent theinner zone 36, and an optional perimeter zone or outer portion 40. Theintermediate zone 38 preferably surrounds inner zone 36, and theperimeter zone 40 preferably surrounds the intermediate zone 38. Theinner zone 36 is a contiguous zone located on the hitting face 16 andcontains a geometric center (“GC”) of the hitting face. As shown, innerzone 36 and its concentric zones have a generally elliptical shape witha major axis in the direction of high heel to low toe. As used herein,the term “ellipse” or “elliptical” refers to non-circular shapes thathave discernable major axis and minor axis, and include, but are notlimited to, any quadrilateral shapes, geometrical ellipses,quadrilateral shapes with one or more rounded corner(s) andunsymmetrical elliptical shapes. Also, the term “concentric” refers toshapes that substantially encircle or surround other shapes. The “majoraxis” is defined as the axis coinciding with the longest length that canbe drawn through the non-circular shapes without intersecting theperimeter of the shapes at more than two locations, i.e., at the startand end points of said length. The “minor axis” is orthogonal to themajor axis at or near its midpoint.

The major axis of inner portion 36 forms an angle, θ, with the shaftaxis, SHA. Preferably, angle θ is between about 10° to about 60°, morepreferably between about 20° and about 50°, and most preferably betweenabout 25° and about 45°. Additionally, the ratio of the length of themajor axis to the length of minor axis is preferably greater than 1.0and more preferably less than about 6.0.

Preferably, zones 36, 38 and 40 are concentric to each other withinhitting face 16. The inner zone 36 has a first thickness T₁. Theintermediate zone 38 has a second thickness T₂. The first thickness T₁is greater than the second thickness T₂. Typically, when the club headis cast, the perimeter zone 40 is thicker than the intermediate zone 38.Alternatively, the hitting face may also be forged. However, the presentinvention is not limited to any manufacturing technique. T₁ may rangefrom about 1.5 mm to about 7.5 mm and T₂ may range from about 0.8 mm toabout 3.0 mm. Preferably, the first thickness T₁ is equal to about oneand a half (1.5) times the thickness T₂ to about four (4) times thethickness T₂.

The thickness relationships between the zones 36, 38, and 40 areprovided so that a predetermined relationship exists between flexuralstiffness exhibited by each of the zones. For clubs that have a hittingface made from a single material, such as titanium or titanium alloy,the area of highest thickness corresponds to the portion with thehighest flexural stiffness. Flexural stiffness (FS) of each portion isdefined as:FS=E(t ³),where E is the elastic modulus or Young's modulus of the material of theportion and t is the thickness of the portion. Young's modulus oftitanium is about 16.5×10⁶ lbs/in², and thickness is typically measuredin inch. Hence, FS as used in this application has the unit of lb·in.

The inner zone 36 has a first flexural stiffness FS₁. The intermediatezone 38 has a second flexural stiffness FS₂. The perimeter zone 40 has athird flexural stiffness FS₃. The predetermined relationship between theportions is that the first flexural stiffness FS₁ is substantiallygreater than the second flexural stiffness FS₂, and the optional thirdflexural stiffness FS₃ is substantially greater than the second flexuralstiffness FS₂. Preferably, the first flexural stiffness FS₁ is at leastthree times greater than the second flexural stiffness FS₂, i.e.,(FS₁/FS₂)≧3. When the above ratio of flexural stiffness is less thanthree, the inner zone sustains excessive deformation during impact andaccuracy of the club is diminished. More preferably, the first flexuralstiffness FS₁ is about six (6) to twelve (12) times greater than thesecond flexural stiffness FS₂. Most preferably, the first flexuralstiffness FS₁ is about eight (8) times greater than the second flexuralstiffness FS₂. Preferably, the third flexural stiffness FS₃ is at leasttwo times greater than the second flexural stiffness FS₂, i.e.,(FS₃/FS₂)≧2.

Alternatively, the flexural stiffness, FS₁, FS₂ or FS₃, can bedetermined for two combined adjacent zones, so long as the preferredratio (FS₁/FS₂)≧3 or (FS₃/FS₂)≧2 is satisfied. For example, FS₁, can becalculated to include both zones 36 and 38, and FS₃ can be calculated toinclude both zones 38 and 40.

The thickness of the zones, T₁ and T₂, may be constant within the zoneas illustrated in FIGS. 3A and 3B, or may vary within the zone asillustrated in FIGS. 3C and 3D. For the purpose of determining FS, whenthe thickness varies, a weighted average thickness is calculated. Thedetermination of FS when the thickness varies or when the material isanisotropic is fully discussed in the parent patent application, whichhas already been incorporated by reference in its entirety.

In club head 10 (as shown in FIGS. 3–3D), the above flexural stiffnessrelationships are achieved by selecting a certain material with aparticular elastic modulus and varying the thickness of the zones. Inanother embodiment, the flexural stiffness relationships can be achievedby varying the materials of the zones with respect to one another sothat the zones have different elastic moduli and the thickness ischanged accordingly. Thus, the thickness of the zones can be the same ordifferent depending on the elastic modulus of the material of each zone.It is also possible to obtain the required flexural stiffness ratiothrough the use of structural ribs, reinforcing plates, and thicknessparameters.

Quantitatively, it is preferred that the first flexural stiffness FS₁ isgreater than 25,000 lb-in. When the first flexural stiffness is lessthan 25,000 lb-in excessive deformation of the inner region can occurduring impact and accuracy is diminished. More preferably, the firstflexural stiffness FS₁ is greater than 55,000 lb-in. Preferably, thesecond flexural stiffness FS₂ is less than 16,000 lb-in. When the secondflexural stiffness is greater than 16,000 lb-in, the resultant ballvelocity is reduced. More preferably, the second flexural stiffness FS₂is less than 10,000 lb-in and, most preferably, less than 7,000 lb-in.

Referring to FIG. 3, it is preferred that inner zone 36 has an area thatis between about 15% and about 60% of the exterior surface area 32. Thepercentage of face area is computed by dividing the area of each zone36, 38, or 40 by the total face area of exterior surface 32. It shouldbe noted that the face area of exterior surface 32 is equivalent to thetotal area of zones 36, 38, and 40. When the inner zone 36 is less than15% of the total face area, then accuracy can be diminished. When innerportion 36 is greater than 60% of the face area 32, then the coefficientof restitution can be diminished.

Referring again to FIG. 1, the club head 10 is further formed so that acenter of gravity of the club head has a predetermined relationship withrespect to a Cartesian coordinate system with its center located onhitting face 16 and coincident with the geometric center GC of the face16. The hitting face 16 includes a vertical centerline VCL and ahorizontal centerline HCL perpendicular thereto. The geometric center(GC) of hitting face 16 is located at the intersection of centerlinesVCL and HCL. The VCL and HCL are co-linear with the X-axis and theZ-axis of a Cartesian coordinate system, described below. Preferably,the GC of the inner zone 36 is spaced from the GC of hitting face 16 bya distance of less than about 0.10 inch, more preferably less than about0.05 inch and most preferably less than about 0.025 inch. The GC ofinner zone 36 may be coincident with the GC of hitting face 16. The GCof inner zone 36 can be defined as the intersection between the majoraxis and the minor axis of the zone.

The Cartesian coordinate system is defined as having the origincoincident with the geometric center of the hitting face. The hittingface is not a rectilinear plane, but due to the bulge and roll radii itis a curvilinear surface. The X-axis is a horizontal axis lying tangentto the geometric center of the hitting face with the positive directiontoward the heel of the club. The Y-axis is another horizontal axisorthogonal to the X-axis with the positive direction toward the rear ofthe club. The Z-axis is a vertical axis orthogonal to both the X-axisand Y-axis with the positive direction toward the crown of the club.

The center of gravity is preferably located behind and lower than thegeometric center of the face when the club head is resting on a flatsurface (i.e., at its natural loft). In one preferred embodiment, thecenter of gravity of club head 10 is spaced from the geometric centeralong the Z-axis between about −0.050 inch and about −0.150 inch, morepreferably about −0.110 inch. The center of gravity is preferably spacedabout ±0.050 inch, more preferably about 0.015 inch, from the geometriccenter along the X-axis. The center of gravity is preferably spacedabout 2.0 inches or less and more preferably about 1.35 inches or lessfrom the geometric center along the Y-axis.

The center of gravity for the club head can be achieved by controllingthe configuration and dimensions of the club head in addition to addingpredetermined weights to the sole plate or to the club head. Other knownmethods of weight manipulation can be used to achieve the inventivecenter of gravity location as set forth above.

FIG. 6 illustrates another embodiment of the present invention. Centralzone 36 has a generally parallelogram shape, such that the oppositesides are generally parallel and the angles formed between adjacentsides are rounded. More specifically, the acute angle α of central zone36 is preferably between 40° and 85°. Additionally, the major axis ofcentral zone 36, as shown, forms an angle β with the HCL, whichpreferably is between 5° and 45°. The major axis is the line connectingthe two acute angles of the parallelogram. Similar to the embodimentsdisclosed above, intermediate zone 38 surrounds central zone 36, and therelative thickness and ratio of FS between zone 36 and zone 38 followthe relationships discussed above.

As shown in FIG. 7, central zone 36 can be an ellipse while intermediatezone 38 can have a generally parallelogram shape. Conversely, centralzone 36 can have a generally parallelogram shape, while intermediatezone 38 can be an ellipse. Furthermore, as illustrated intermediate zone38 may have varying width.

In accordance to another aspect of the present invention, hitting face16 may comprise a face insert 42 and face support 44, as shown in FIG.8. In this embodiment, hitting face 16 is delineated from crown 28, toe18, sole 22 and heel 20 by parting line 46. Central zone 36 ispreferably disposed on the back side of face insert 42, and, as shown,has a generally parallelogram shape. Intermediate zone 38, designated as38 ₁ and 38 ₂, can be disposed partially on face insert 42 and partiallyon face support 44. A transition zone 37 having variable thickness isdisposed between central zone 36 and intermediate zone 38. Preferably,the thickness of central zone 36 is reduced to the lesser thickness ofintermediate zone 38 within transition zone 37. This reduces any localstress-strain caused by impacts with golf balls due to abrupt changes inthickness. Face support 44 defines hole 48, which is bordered by rim 50.Face insert 42 can be attached to face support 44 by welding at oraround rim 50. For the purpose of determining the FS ratio for thisembodiment, the FS₁ of the inner zone includes both zone 36 and zone 37.

In accordance to another aspect of the invention, the face insert mayinclude one or more side walls, wherein the side walls may form part ofthe crown and/or part of the sole. As shown in FIG. 9, face insert 52comprises central zone 36, transition zone 37, a portion of intermediatezone 38, partial crown portion 54 and partial sole portion 56. Club head10 correspondingly defines cavity 58 sized and dimensioned to receiveface insert 52. Face insert 52 is preferably welded to club head 10.Face insert 52 together with face support 60 forms hitting face 16.Similar to the embodiment illustrated in FIG. 8, intermediate zone 38,designated as 38 ₁, and 38 ₂, can be disposed partially on face insert52 and partially on face support 60.

EXAMPLE

In this example, hitting face 16 has the following construction. Thecentral zone 36 has a substantially parallelogram shape, as shown inFIG. 10( a), with a major axis measuring about 3 inches and a minor axisabout 0.75 inches with a thickness T₁, of about 0.120 inch. The centralzone 36 has a concentric transition zone 37 with a similar shape as thecentral zone 36. The intermediate zone 38 surrounds the central andtransition zones with a thickness T₂ of 0.080 inch and comprises theremainder of the face hitting area. There is no perimeter zone 40included in this example. The major axis of zone 36 substantiallycoincides with the major axis of zone 38, and these two major axes formangle theta (θ) of about 50° with the shaft axis. Furthermore, zones 36and 37 comprise about 18% of the total face surface area. A singlehomogeneous material, preferably a titanium alloy, with a Young'smodulus (E) of approximately 16.5×106 lbs/in² is used. In this example,the (FS1/FS2) ratio is 3.4 when FS1 includes both zones 36 and 37 andFS2 includes zone 38.

The test results were generated using computational techniques, whichinclude finite element analysis models. In the computer model, thefollowing assumptions were made: club head loft of 9°; club head mass of195 grams; and club head material is 6AL-4V titanium alloy. The golfball used in the model was a two-piece solid ball. Finite element modelswere used to predict ball launch conditions and a trajectory model wasused to predict distance and landing area. The impact condition used forclub coefficient of restitution (COR) tests was consistent with the USGARules for Golf, specifically, Rule 4-1e Appendix II Revision 2 datedFeb. 8, 1999.

Distributions of coefficient of restitution (COR) are shown in FIGS. 10(b) and 10(c). The lines indicate contour lines, similar to the contourlines in topography maps or weather maps, and indicate lines of constantCOR (hereinafter iso-COR lines). The innermost contour line indicatesthe highest COR region on the hitting face and outer contour linesindicate lower COR regions on the hitting face. FIG. 10( b) representsthe iso-COR contours for a conventional club having a hitting face withuniform thickness, and FIG. 10( c) represents the iso-COR contours ofthe inventive club described in this Example.

COR or coefficient of restitution is one way of measuring ballresiliency. COR is the ratio of the velocity of separation to thevelocity of approach. In this model, therefore, COR was determined usingthe following formula:(v_(club-post)−v_(ball-post))/(v_(ball-pre)−v_(club-pre))where,

-   -   v_(club-post) represents the velocity of the club after impact;    -   v_(ball-post) represents the velocity of the ball after impact;    -   v_(club-pre) represents the velocity of the club before impact        (a value of zero for USGA COR conditions); and    -   v_(ball-post) represents the velocity of the ball before impact.

COR, in general, depends on the shape and material properties of thecolliding bodies. A perfectly elastic impact has a COR of one (1.0),indicating that no energy is lost, while a perfectly inelastic orperfectly plastic impact has a COR of zero (0.0), indicating that thecolliding bodies did not separate after impact resulting in a maximumloss of energy. Consequently, high COR values are indicative of greaterball velocity and distance.

The iso-COR contour lines generated by the computational analysis areshown within a rectangle having dimensions of 0.5 inch by 1.0 inch, astypically used in the art. Within this rectangle, the inventive clubhead exhibits relatively high and substantially uniform COR values. TheCOR values are measured at nine points within this rectangle, i.e., thecorners of the rectangle, mid-points of the sides and the geometriccenter of the rectangle. Additionally, the geometric center of thisrectangular measurement zone preferably coincides with the geometriccenter of the hitting face of the club. In this example, the lowest CORwithin this measurement zone is 0.828 and the peak COR is 0.865.According to the present invention, the lowest COR is within 93% of thepeak COR. This advantageously produces a hitting face with asubstantially uniform COR and large “sweet spot”.

The iso-COR contour lines of the conventional club shown in FIG. 10( b)follow a substantially elliptical pattern. Furthermore, the center ofthe innermost iso-COR contour line, which has the highest COR value, isoffset from the geometric center of the rectangular measurement zone,indicating a reduction in COR. The major axis of these contour lines issubstantially horizontal.

The iso-COR contour lines for the inventive club also follow anelliptical pattern, and as shown in FIG. 10( c), the major axis of thepattern does not coincide with the horizontal center line, HCL, of thehitting face. The test results indicate that the major axis of theiso-COR pattern makes an angle, delta(δ), with the HCL. The angle δ isat least 5°, and more preferably at least 7° in the direction from hightoe to low heel. While the major axis of central zone 36 with thehighest FS runs substantially from high heel to low toe, the major axisof the iso-COR contours runs substantially in a different direction,i.e., from high toe to low heel, which advantageously coincides with thetypical hit distribution that golfers make on the hitting face,discussed above. Furthermore, the center of the innermost iso-CORcontour line is closer to the geometrical center of the rectangularmeasurement zone, indicating a higher peak COR value.

Without being limited to any particular theory, the inventors of thepresent invention observe that when an elliptical area of high thicknessor high FS is present at or near the center of the hitting face withareas of less thickness or lower FS surrounding it, the iso-COR contourlines generally form an elliptical shape where the major axis of theiso-COR contours forms an angle with the major axis of the areas of highthickness or high FS. This arrangement of inner and intermediate zonesforms a zone of relatively high flexural stiffness in the direction ofhigh heel to low toe thereby creating high resilience in the directionof high toe to low heel. In other words, this arrangement creates agradient of flexural stiffness in the direction of high toe to low heeland produces a desirable effect of manipulating resilience or highercoefficient of restitution (COR) in that direction. This area ofimproved coefficient of restitution advantageously coincides with theball impact pattern that golfers typically make on the hitting face.

While various descriptions of the present invention are described above,it should be understood that the various features of each embodiment canbe used alone or in any combination thereof. Therefore, this inventionis not to be limited to only the specifically preferred embodimentsdepicted herein. Further, it should be understood that variations andmodifications within the spirit and scope of the invention may occur tothose skilled in the art to which the invention pertains. For example,the face and/or individual zones can have thickness variations in astep-wise or continuous fashion. Other modifications include a perimeterzone that has a thickness that is greater than or less than theadjacent, intermediate zone. In addition, the shapes of the central,intermediate, and perimeter zones are not limited to those disclosedherein. Accordingly, all expedient modifications readily attainable byone versed in the art from the disclosure set forth herein that arewithin the scope and spirit of the present invention are to be includedas further embodiments of the present invention. The scope of thepresent invention is accordingly defined as set forth in the appendedclaims.

1. A golf club head comprising: a face insert and a face support, theface insert and the face support form a hitting face; the hitting facecomprises an inner zone having a generally parallelogram shape; thehitting face comprises a first flexural stiffness having a major axisthat aligns substantially in the direction of high heel to low toe andan intermediate zone having a second flexural stiffness, wherein thefirst flexural stiffness is higher than the second flexural stiffnessand wherein the major axis of the paralleogram inner zone forms a firstangle in the range of about 10° to about 60° with a shaft axis of theclub head.
 2. The golf club head of claim 1, wherein the face supportdefines a cavity sized and dimensioned to receive the face insert. 3.The golf club head of claim 2, wherein said cavity is located on thehitting face.
 4. The golf club head of claim 1, wherein the golf clubhead defines a cavity sized and dimensioned to receive the face insert.5. The golf club head of claim 1, wherein the face insert comprises atleast one side wall.
 6. The golf club head of claim 5, wherein the atleast one side wall is a partial crown portion.
 7. The golf club head ofclaim 5, wherein the at least one side wall is a partial sole portion.8. The golf club of claim 1, wherein the first angle is about 20° toabout 50°.
 9. The golf club of claim 1, wherein the first angle is about25° to about 45°.